Diamond grinding wheels are usually manufactured by metal bond, vitrified bond or resin bond, wherein the metal-bonded grinding wheel has good profile maintaining capability, ideal service life and higher grinding efficiency, and thereby is applied broadly in production fields of nonferrous metallic materials and non-metallic materials, and etc., such as stone, ceramic, refractory materials, hard alloys, magnetic materials and semiconductor materials, and etc.
The metal bonded diamond grinding wheel is usually manufactured by powder metallurgy, and the manufacturing process thereof mainly comprises materials mixing, compression molding, sintering, post-processing and the like. The preparation process directly affects the working performance of the metal-bonded diamond grinding wheel. Currently there have been three major preparation methods for metal-bonded grinding wheel stocks, i.e. cold compression molding-sintering, hot compression molding-sintering, and semi-hot compression molding-sintering.
In the cold compression molding-sintering process, molded materials are applied a certain pressure in a steel mould so as to be pressed into stocks. After the mould is removed, the stocks are sintered in a furnace without pressure. The main disadvantages of this method lie in the high pressure required for molding, long time for sintering, large energy consumption, and poor mechanical and utility performances of the product. Specifically, it will take a large amount of energy to sinter the stocks in the pressure-less sintering process to achieve the desire purpose. The temperature for sintering maintains for from one to two hours, and the production cycle is too long. Therefore, at present this process is seldom applied.
In general, for the hot compression molding-sintering method, there are two approaches, i.e. medium frequency induction heating and high-current resistance heating. In the hot compression molding-sintering process, the molded materials are often heated and compressed simultaneously in a graphite mould (i.e. to be hot compressed-sintered directly). Alternatively, the molded materials may be cold compressed in a steel mould into stocks having a certain density and strength, and then hot compressed-sintered in the graphite mould. The hot compression molding-sintering method has the following disadvantages: firstly, the size of the prepared grinding tools is limited by the graphite mould, and usually has a diameter of no more than 300 mm; secondly, large amounts of energy are consumed during the medium frequency induction heating and high-current resistance heating processes; thirdly, the quantity of products per each sintering process is limited, and the production efficiency is low.
In the semi-hot compression molding-sintering method, molded materials are pre-pressed in a steel mould into stocks having a certain density and strength, then the stocks, are sintered together with the mould or an altered outer mould without pressure. After the sintering is finished, the stocks are moved out of the furnace and compressed to a desired density. Generally, this method is applicable to grinding tools having relatively large sizes, and its major disadvantages lie in that the temperature for heating is required to maintain for about 30 minutes, and the quantities of products sintered is about one to ten each time, which results in its large energy consumption and low production efficiency.
A bond system employed by the aforementioned methods for producing the metal-bonded diamond grinding wheel mainly comprises Cu—Sn system, such as the one applied in the Japanese Patent Application JP58-217271; Ni—Cu—Sn system, such as the one applied in the Chinese Patent Application CN200410031285.1; and Al—Cu system, such as the one applied in the Chinese Patent Application CN200610037510.1. The sintering methods with these bond systems are direct hot compression molding-sintering or semi-hot compression molding-sintering, both of which are to achieve the sintering process by providing the external heat. To prevent the diamond from graphitization, the sintering temperature is usually controlled no higher than 900□. These bond systems can neither initiate exothermic reaction during the sintering process, nor form carbides between the bond and the grinded diamond, thereby can not achieve the firm bonding. Strong carbide formers added to the metal bond may form a carbide layer with the surface of diamond, which will improve the binding force of the bond on the diamond. However, typically a high temperature of 1200° C. will be required to form the carbide layer. Therefore, under conventional sintering conditions, it is very difficult for the strong carbide formers and the surface of diamond to form a continuous and uniform carbide layer.